WO1996008221A1

WO1996008221A1 - Surgical instrument

Info

Publication number: WO1996008221A1
Application number: PCT/GB1995/002167
Authority: WO
Inventors: William Frederick Ian Shepherd
Original assignee: Sterimedix Limited
Priority date: 1994-09-14
Filing date: 1995-09-13
Publication date: 1996-03-21
Also published as: GB9418449D0; GB2293104A; AU3480395A

Abstract

An irrigation/aspiration cannula (1) for use in cataract extraction having at its working tip (2) an unsheathed rotary cutting bit (3) which is disposed for irrigation fluid flowing from the irrigation port (4) to the aspiration port (5) to pass over and around the cutting bit (3) and is coupled to a rotary drive shaft (9) located outside the aspiration tube (7).

Description

SURGICAL INSTRUMENT

The present invention relates to a surgical instrument. More particularly it relates to a surgical instrument useful for segmentation of a medium to hard nucleus in cataract surgery.

Cataracts may be extracted from the eye by making an incision through the cornea, limbus or sclera and into the capsular bag containing the lens. The lens nucleus is removed from the capsular bag, for example by loosening it from the bag and delivering it through the incision.

The incision required to remove the whole nucleus is around 9.0 mm, and normally the lens is balanced upon an irrigation "spoon" Vectis or Lens Loop cannula.

The disadvantage of this very well used procedure is that the 9.0 mm incision is considered too large and it is generally agreed that an incision of 3.0-3.5mm offers many advantages:

Increased safety of day surgery cataract operations Enhanced Visual rehabilitation Lower Incidence of Post-operative Trauma Lower Incident of Astigmatism

Lower Incidence of Infection No need for micro-suture

The main method of working through a small incision is by the use of a phacoe ulsification machine. This is a costly machine which breaks up the lens matter by ultrasound, and automatically removes the debris through its tips.

Around 20% of procedures of cataract surgery in Europe use phacoemulsification. The present inventor considers that there are certain problems associated with phacoemulsification:

High Capital Cost Cost Expensive Disposable Tips

Risk of Damage to Endothelium or Posterior Capsule Protracted learning curve

Other methods of fragmentation of the nucleus have been tried by the present inventor and others, but none has proved satisfactory.- Amongst the others are:

Cutting platforms

Nucleus crushers

Wire or Nylon Lasoos

Various proposals have been made for cataract removal instruments involving a rotary cutting bit, but no such instrument is believed to be in widespread use, if used at all.

The cutting bit of prior art instruments is completely or partially enclosed, as described in US patents 3732858, 3844272, 3937222, 3945375, 3976077, 4320761 , 4428748 and 5019036. In these prior art devices, fluid and debris is aspirated through a tube which surrounds, or even constitutes, the cutting bit. It is believed that the prior art instruments have not met with success because of performance and/or cost disadvantages arising from their designs. Thus, US 3976077 proposes a device which aims to overcome disadvantages in the prior art resulting from debris gaining access to the interior of the device and causing the drive shaft to bind. The device of US 3976077 includes a complex and expensive bearing arrangement to exclude fluid and debris from its interior and uses the cutting bit to effect aspiration of fluid through a tube portion partially sheathing the cutting bit. The present invention relates to a surgical instrument, suitably referred to as a cannula, which may be used effectively and economically for extracting cataracts.

In one aspect, the present invention provides a surgical instrument for use in eye surgery, having a working tip and comprising an irrigation tube having defined therein an irrigation port at the working tip of the instrument, an aspiration tube having defined therein an aspiration port at the working tip of the instrument, and a rotary cutting bit arranged externally of the instrument at its working tip and coupled to a rotary drive shaft disposed outside the aspiration tube, the irrigation and aspiration ports being arranged such that in use irrigation fluid flows from the irrigation port, over and around the cutting bit and into the aspiration port.

The rotary drive shaft is in use connected to drive means. The shaft is therefore suitably provided at its end remote from the cutting bit with means adapted to couple it to drive means. The cutting bit and the drive shaft are desirably formed in one piece.

In one class of embodiments the longitudinal axes of the irrigation and aspiration tubes and the axis of rotation of the cutting bit are coplanar.

One of the irrigation and aspiration tubes may extend within the interior of the other. Normally the aspiration tube extends within the bore of the irrigation tube; a third tube, parallel to the aspiration tube, may adjoin the aspiration rube. In preferred embodiments the irrigation tube has an open end defining the irrigation port and the aspiration tube has an open end defining the aspiration port. In such preferred embodiments the open end of the aspiration tube is located at the open end of the irrigation tube. The cutting bit projects from the open end of the irrigation tube to the side of the aspiration tube. The cutting bit is connected with a rotary drive shaft which extends within the irrigation tube by the side of the aspiration tube. The rotary drive shaft may be accommodated in the third tube extending alongside the aspiration tube.

In those preferred embodiments in which the aspiration tube extends within the bore of the irrigation tube, the open end of the aspiration tube is preferably directed outwardly, usually by a small angle, as well as forwardly. The forwardmost part of the aspiration tube may be substantially flush with the open end of the irrigation tube. Another preferred feature is the provision of annular inwardly and forwardly directed baffle means at the open end of the irrigation tube; the baffle means is suitably formed by an inwardly directed terminal portion of the side wall of the irrigation tube.

The cutting bit suitably comprises a metal web, one or more edge regions of which may be sharpened. Preferably the web has opposed sides of which one is sharpened to form a cutting edge and a leading end which has defined therein a slit which, when a major face of the web is viewed in plan, is a V-shape, the slit being defined by edge regions of the web at an angle to each other and the one of the edge regions opposed to said cutting edge itself being sharpened to form a cutting edge.

In the embodiments in which the aspiration tube extends within the irrigation tube, the instrument preferably has at a region remote from the working tip a hub member secured to the irrigation tube, as by means of screw threads, for example. The irrigation tube preferably has at its end remote from the working tip a portion of enlarged bore to engage with a hub of complementary size. The hub member preferably has defined therein through hole means (e.g. one or more through holes) through which pass the aspiration tube and the rotary drive shaft. The hub member preferably has defined therein a through hole through which irrigation fluid is in use carried into the irrigation tube, an irrigation fluid feed tube suitably extending through said through hole to contain the irrigation fluid.

In alternative embodiments, the irrigation and aspiration ports are coplanar with each other and with the cutting bit, which has an axis of rotation which passes between the irrigation and aspiration ports. The ports are preferably directed forwardly and outwardly. Preferably, a central tube accommodating the rotary drive shaft is formed between the irrigation and aspiration tubes throughout a length of the cannula (normally more than half the overall length of the cannula) extending from its working tip. The three tubes are coplanar.

In a second aspect of the invention there is provided an irrigation/aspiration cannula for use in ophthalmic surgery having at its working tip an unsheathed rotary cutting bit which is disposed for irrigation fluid flowing from the irrigation port to the aspiration port to pass over and around the cutting bit and is preferably coupled to a rotary drive shaft located outside the aspiration tube. The cannula of this aspect of the invention may suitably possess one or any combination of preferred features of the first aspect of the invention.

In a third aspect the invention relates to a surgical instrument for use in cataract extraction which comprises a shaft portion. The shaft portion has a free end at which is the working tip of the instrument. The shaft portion comprises an outer irrigation tube having at the working tip an open end defining an irrigation port. Within the irrigation tube extend in side-by-side relationship an aspiration tube and a rotary drive tube, both of which have an open end at the open end of the irrigation tube. The open end of the aspiration tube defines an aspiration port. The rotary drive tube accommodates a rotary drive wire from which extends a rotary cutting bit which is located at the working tip externally of the irrigation and aspiration tubes. The irrigation and aspiration ports are arranged such that in use a liquid flow path is formed between them which goes across and around the cutting bit. The drive wire is capable of being coupled to drive means and, to that end, may be provided with means (e.g. a chuck locator) for coupling it to drive means.

In a fourth aspect the invention relates to a surgical instrument for use in cataract extraction which comprises an elongate shaft portion. The shaft portion comprises three coplanar tubes: a central tube and lateral irrigation and aspiration tubes. The shaft portion has a working tip, whereat there is an external rotary cutting bit from which extends a rotary drive wire accommodated in the central tube. The drive wire is provided at its end remote from the cutting bit with means (e.g. a chuck locator) for coupling it to drive means. The irrigation and aspiration tubes are open at the working tip to form irrigation and aspiration ports, arranged such that in use a liquid flow path is formed between them which goes across the cutting bit.

In one modification of the fourth aspect of the invention, the shaft portion comprises side-by-side irrigation and aspiration tubes, the rotary drive wire being accommodated in the irrigation tube.

In those embodiments of the fourth aspect comprising three coplanar tubes the irrigation and aspiration tubes at the working tip preferably have open end faces extending outwardly and rearwardly from the central tube, thereby defining outwardly and forwardly directed irrigation and aspiration ports.

In a fifth aspect, there is provided a method for removing a lens from an eye, comprising the steps of:

(a) providing a surgical instrument having a working tip and comprising: an irrigation tube having defined therein an irrigation port at the working tip of the instrument; an aspiration tube having defined therein an aspiration port at the working tip of the instrument; and a rotary cutting bit arranged externally of the instrument at its working tip and coupled to a rotary drive shaft disposed outside the aspiration tube, the irrigation and aspiration ports being arranged such that in use irrigation fluid flows from the irrigation port, over and around the cutting bit and into the aspiration port,

(b) making incisions in tissue to the anterior of the lens to enable access of the working tip of the cannula to the lens, (c) contacting the lens with the cutting bit of the cannula, and

(d) causing the cutting bit to rotate whilst it is applied to the lens, irrigation fluid is passed through said irrigation tube, and irrigation fluid and debris is aspirated through said aspiration tube.

The invention includes an irrigation/aspiration cannula having at its end tip and working concurrently in use:

a completely unsheathed cutting bit revolved by the use of a drill or other drive means, typically in a clock-wise direction at speeds of up to 3,000 rpm, an aspiration port through which is sucked liquid and debris into an aspiration tube, an irrigation port through which balanced salt solution or other liquid conveyed by an irrigation tube flows to pass across and around the cutting bit.

In effect the aspiration port removes the liquid which has passed over the cutting bit picking up the fragmented particles of nucleus.

Also included is an irrigation/aspiration cannula having a rotary cutting bit at its working tip and a rotary drive shaft coupled to the cutting bit, wherein the cutting bit (whether sheathed or unsheathed) and the drive shaft are both outside the aspiration tube.

The present invention is further described by way of example only with reference to the accompanying drawings, in which:

Figure 1 is an exploded plan view of a cannula of the invention;

Figure 2 is a side view of the cannula of Figure 1 in which the irrigation tube is not shown; Figure 3 is an enlarged view of a tip portion of the cannula of Figure 1 ; Figure 4 is a schematic illustration of a patient's eye having the cannula of Figure 1 inserted through a small incision; and

Figure 5 is a plan view of a cannula according to a second embodiment of the invention.

The drawings illustrate a surgical instrument according to the invention. The instrument therefore comprises an irrigation/aspiration cannula 1 comprising at its tip 2 a rotary cutting bit 3 as well as an irrigation port 4 and an aspiration port 5. The cutting bit 3 is coupled to a rotary drive shaft 9. The irrigation and aspiration ports 4, 5 are arranged such that in use irrigation fluid flows out of the irrigation port 4, passes over and around the cutting bit 3 and into the aspiration port 5. The instrument is characterised in that either the cutting bit 3 is arranged externally of the instrument or the cutting bit 3 and the drive shaft 9 are disposed outside the aspiration tube.

Looking now in more detail at the illustrated embodiment, the irrigation and aspiration ports 4, 5 communicate respectively with irrigation and aspiration tubes 6, 7. The irrigation tube 6 is shown in the illustrated embodiment to be disposed around the aspiration tube 7 and a rotary drive tube 8 along a distal shaft portion of the cannula 1. The drive tube 8 accommodates the rotary drive shaft or wire 9 having the cutting bit 3 provided at its end, as shown in Figure 3. The wire 9 and the cutting bit 3 are preferably formed as one piece, the wire 9 having been shaped to form the cutting bit 3. The side wall of the drive tube 8 is preferably closed.

The shape of the cutting bit 3 is not critical to the invention. As shown in Figure 3 it may be generally planar (flat) and optionally have opposed side edges 10, 11 parallel with the axis of rotation. It may have one or more sharpened edge regions.

One 10 of the opposed side edges 10, 11 is chamfered to form a cutting edge. The leading end of the cutting bit 3 has defined therein a V-shaped groove such that the cutting bit presents angular edges 12, 13. The angular edge 13 opposed to the cutting edge 10 is also chamfered to form a cutting edge.

The cannula 1 is provided at a base region remote from the working tip with a hub member 14 having an external thread 15. The irrigation tube 6 has a portion 16 of enlarged diameter at its end opposite the irrigation port 4. The enlarged portion 16 is internally threaded at 17 for screwing on the hub member 14. The irrigation mbe 6 may alternatively be secured to the hub member 14 by another arrangement. The invention is, however, not restricted to the interengagement of the irrigation mbe 6 with a hub member 14 for securing the irrigation mbe 6 to the remainder of the cannula 1.

The hub member 14 is connected with the aspiration mbe 7 and drive mbe 8. Specifically, in the illustrated embodiment a through hole is formed in the hub member 14 to accommodate securely the aspiration tube 7. A through hole also securely accommodates the drive tube 8. An irrigation fluid feed tube 18 passes through the hub member 14. The feed mbe 18 terminates at an outlet 19 disposed inside the irrigation mbe 6; in other embodiments irrigation fluid flows directly into the irrigation mbe 6 via a through hole in the hub member. The feed mbe 18 need not be coplanar with aspiration and drive tubes 7, 8; in one preferred class of embodiments the feed mbe 18 is located above or below the aspiration and drive tubes 7, 8.

The proximal end region of the drive shaft 9 passes through a chuck locator 20, i.e. a male member for push fitting into the chuck of a drive means (not shown) for driving the wire 9 and the cutting bit 3. In alternative embodiments the chuck connector 20 is replaced by other means for connecting the cutting bit 3 to a rotary drive means through the shaft 9 or is dispensed with. The rotary drive means may be a surgical drill. A suitable drill is that sold under the trade mark ORTHO- BURR (obtainable from Xomed-Treace Inc, 6743 Southport Drive North, Jacksonville, Florida 32216, USA). As illustrated in Figure 1 , the drive shaft 9 is suitably provided with a region of enlarged diameter at its proximal end, to be received in a chuck.

The feed mbe 18 and aspiration mbe 7 diverge outwardly from the shaft or wire 9 at a location towards the base of the cannula 1 and preferably as close to the chuck locator 20 as practicably possible. In use the feed and aspiration tubes 18,

7 are connected to plastics (e.g. silicone) tubing. To this end the irrigation feed mbe 18 and aspiration mbe 7 are suitably provided with push-fit connectors 21, 22 for silicone tubing and a distal hub to allow a syringe or other aspiration means to be connected.

Looking now in more detail at the working tip 2 of the surgical instrument (cannula), the configuration and orientation of the irrigation and aspiration ports 4, 5 is not critical to the invention, provided that they satisfactorily enable irrigation liquid to pass over and around the cutting bit 3 and, together with entrained debris, to be removed through the aspiration port 4 whilst not unacceptably interfering with the functioning of the cutting bit 3.

Most surprisingly, the optimum arrangement found for the irrigation and aspiration ports 4, 5 is as shown in Figure 3. The open ends of the irrigation and aspiration tubes 6, 7 are juxtaposed. The end of the irrigation tube 6 lies on a diametric plane. A terminal portion 23 of the irrigation tube wall is curved somewhat inwardly to form inwardly and forwardly oriented annular baffle means. The aspiration port 5 may face forwardly but more preferably faces at a small outward angle as well as forwardly and at its forwardmost point is substantially flush with the end of the irrigation mbe 6. The aspiration port 5 is preferably at an angle of from 70° to 90° to the longitudinal axis of the working tip, and is more preferably at an angle of 75° to 85°, e.g. about 80°. The end of the drive mbe

8 is also substantially flush with the end of the irrigation mbe 6, and lies behind the cutting bit 3 which is disposed outside the irrigation mbe 6 to form the leading part of the cannula 1. The entire cutting bit is unsheathed. The irrigating liquid in use exits the irrigating mbe 6 by the port 4 defined in the irrigating mbe 6 by the tube wall and the aspirating and rotary drive tubes 7, 8.

The invention is not restricted as to the dimensions of the cannula. The length a (Figure 1) from the forwardmost tip of the irrigation mbe 6 to the proximal end of the chuck locator 20 is suitably 32 to 60 mm, especially 48 mm. The distance b from the foremost tip of the irrigation mbe 6 to the commencement of widening of the mbe is suitably from 10 to 18 mm, especially 14 mm.

The cutting bit 3 suitably has a maximum diameter d of from 1.0 to 1.4 mm, especially about 1.2 mm, and suitably a maximum dimension c from front to rear of 0.4 to 1.4 mm, especially 0.9 mm.

The cannula or surgical instrument of the invention is useful for fragmenting the medium to hard nucleus and removing the fragments by the aspiration mbe incorporated in the cannula, optionally with the additional use of a wide-bodied aspiration cannula after fragmentation.

Figure 4 is a schematic illustration of a patient's eye as viewed in cross-section. The eye comprises a sclera A and a cornea B, at the junction of which is a limbus C. The shaded area E represents an iris, a pupil D defined by the iris E being dilated. Behind the pupil D lies a lens F in a capsular bag G. A capsularhexis shown by dotted line H is disposed anteriorly of the capsular bag G. A retina I is at the back of the eye. An incision J has been made in the sclera A, the incision being shown to be in the part of the sclera A distal to the patient's feet. An end portion of a cannula 1 has been inserted through the incision J.

The cutting bit is revolved as irrigation and aspiration are performed. As the cutting bit sculpts and fragments the lens, the debris is withdrawn through the aspiration mbe. The cutting bit is typically revolved at a rotational speed of between 1 ,000 rpm and 5,000 rpm and more usually at between 1,000 and 4,000 rpm, e.g. about 1,300 or about 3,000 rpm. The surgical instrument of the invention is suitably made of stainless steel, as is known in the art. Thus the feed mbe 18, the aspiration mbe 7, the rotary drive mbe 8 and the hub member 14 are suitably formed separately from stainless steel before the three mbes 7, 8, 18 are positioned in the hollow interior of the hub member 14 and soldered into place. The three mbes 7, 8, 18 may be soldered together to form a unit before insertion into the hub member 14. Customarily the solder has a high silver content, normally of at least 50 wt%, e.g. 52-54 wt%.

Figure 5 is a plan view of a second embodiment of the invention. The parts of the cannula of Figure 5 having corresponding parts in the cannula of Figures 1 to 3 have the reference numeral used in Figures 1 to 3 increased by 100.

In Figure 5, the cannula 101 has a shaft portion comprising irrigation, aspiration and rotary drive mbes 106, 107, 108 arranged in a plane. The rotary drive tube 108 is disposed between the other two tubes 106, 107 and accommodates a rotary drive wire 109 formed at the working tip 102 of the cannula 101 into a cutting bit 103, suitably identical to that shown in Figure 1 to 3. The aspirating and irrigating tubes 106 and 107 terminate rearwardly of the cutting bit 103, normally to define forwardly and outwardly facing irrigating and aspirating ports 104, 105. The irrigating and aspirating mbes 106, 107 may diverge outwardly towards the base of the cannula 101, close to a chuck locator 120 on the rotary drive wire 109.

Whilst the invention has been illustrated by instruments having particular arrangements of the irrigation and aspiration tubes, the invention is not limited to such an arrangement. In particular, the invention contemplates that the shaft portion of the cannula may consist of side-by-side irrigation and aspiration mbes, the former of which accommodates a rotary drive wire.

In order to provide for differing depths of eye and different densities of the cataract lens, it is desirable to provide a range of instruments in which one or more of the following features is varied: (i) the gauge of the irrigation mbe, (ii) the gauge of the aspiration tube, and

(iii) the position of the ports in relation to the cutting bit and/or in relation to each other.

Thus, the cannula in the drawings illustrates the principal of the invention but the invention is not limited to a cannula of the particular shape shown in the drawings. What is important is that the instrument enables the combined action of cutting by a rotary bit, irrigation and aspiration to remove the fragmenting pieces of the nucleus.

Claims

1. A surgical instrument for use in eye surgery, having a working tip and comprising an irrigation mbe having defined therein an irrigation port at the working tip of the instrument, an aspiration mbe having defined therein an aspiration port at the working tip of the instrument, and a rotary cutting bit arranged externally of the instrument at its working tip and coupled to a rotary drive shaft disposed outside the aspiration mbe, the irrigation and aspiration ports being arranged such that in use irrigation fluid flows from the irrigation port, over and around the cutting bit and into the aspiration port.

2. An instrument of claim 1, wherein the aspiration mbe extends within the irrigation tube.

3. An instrument of claim 2, wherein the irrigation mbe has an open end defining the irrigation port and the aspiration mbe has an open end defining the aspiration port, the open end of the aspiration mbe being located at the open end of the irrigation mbe and the cutting bit projecting from the open end of the irrigation mbe at a position laterally of the aspiration tube.

4. An instrument of claim 3, wherein the open end of the aspiration mbe is directed outwardly and forwardly.

5. An instrument of claim 3 or claim 4, wherein the forwardmost part of the aspiration mbe is substantially flush with the open end of the irrigation mbe.

6. An instrument of any of claims 2 to 5, wherein annular inwardly and forwardly directed baffle means is provided at the open end of the irrigation mbe.

7. An instrument of claim 6, wherein the baffle means consists of an inwardly directed terminal portion of the wall of the irrigation mbe.

8. An instrument of any of claims 1 to 7, wherein the rotary drive shaft has at a base region remote from the cutting bit means adapted to couple the drive shaft to rotary drive means.

9. An instrument of claim 8, wherein the coupling means comprises a chuck locator for insertion in the chuck of a drill.

10. An instrument of any of claims 1 to 9, wherein the cutting bit is formed in one piece with the drive shaft.

11. An instrument of any of claims 1 to 10, wherein a third mbe, parallel with the aspiration mbe, adjoins the aspiration tube and the rotary drive shaft is accommodated in the third tube.

12. An instrument of any of claims 1 to 11, wherein the instrument has at a region remote from the working tip a hub member connected with the irrigation mbe at an end thereof opposite to said open end.

13. An instrument of claim 12, wherein the hub member has defined therein through hole means through which passes the aspiration mbe.

14. An instrument of claim 12 or claim 13, wherein the hub member has defined therein through hole means through which irrigation fluid is in use carried to the irrigation mbe.

15. An instrument of any of claims 12 to 14, wherein the hub member has defined therein a through hole through which extends the rotary drive shaft.

16. An instrument of claim 1 or claim 2, wherein throughout a length of the cannula extending from its working tip the irrigation and aspiration mbes have defined between them a central tube along which passes the rotary drive shaft, all of which tubes are coplanar.

17. An instrument of claim 1 or claim 2, wherein the irrigation and aspiration ports are disposed side-by-side and the rotational axis of the cutting device passes through the irrigation port.

18. An instrument of any of claims 1 to 17, wherein the cutting bit consists of a flat metal web.

19. An instrument of claim 18, wherein the metal web has opposed sides of which one is sharpened to form a cutting edge and has a leading end having defined therein a slit which, when a major face of the web is viewed in plan, is a V-shape, the slit being defined by edge regions of the web at an angle to each other and the one of the edge regions opposed to said cutting edge itself being sharpened to form a cutting edge.

20. An instrument of any of claims 1 to 19 wherein the cutting bit has a maximum diameter of from 1.0 to 1.4 mm and a maximum length of from 0.4 to 1.4 mm.

21. An instrument of any of claims 1 to 20 which is a cataract extraction cannula.

22. An irrigation/aspiration cannula for use in ophthalmic surgery having at its working tip an unsheathed rotary cutting bit which is disposed for irrigation fluid flowing from the irrigation port to the aspiration port to pass over and around the cutting bit and is coupled to a rotary drive shaft located outside the aspiration mbe.

23. A cannula of claim 22, wherein the cutting bit consists of a flat metal web, the web optionally having opposed sides of which one is sharpened to form a cutting edge and a leading end which has defined therein a slit which, when a major face of the web is viewed in plan, is a V-shape, the slit being defined by edge regions of the web at an angle to each other and the one of the edge regions opposed to said cutting edge itself being shaφened to form a cutting edge, and the cutting bit has a maximum diameter of from 1.0 to 1.4 mm and a maximum length of from 0.4 to 1.4 mm.

24. A surgical instrument for use in cataract extraction, comprising a shaft portion having a free end at which is a working tip of the instrument, the instrument comprising in the shaft portion an outer irrigation mbe having at the working tip an open end defining an irrigation port, and within the irrigation mbe in side-by-side relationship an aspiration mbe and a rotary drive mbe, the aspiration mbe and the rotary drive mbe each having an open end at the open end of the irrigation mbe, the open end of the aspiration mbe defining an aspiration port and the rotary drive mbe accommodating a rotary drive wire from which extends at the working tip a rotary cutting bit located externally of the irrigation and aspiration mbes and which is capable of being coupled to drive means, the irrigation and aspiration ports being arranged such that in use a liquid flow path is formed between them which goes over and around the cutting bit.

25. An instrument of claim 24 which further includes the feature(s) of claim 18 or of claim 18 in combination with one or both of claims 19 and 20.

26. A method for removing a lens from an eye, comprising the steps of:

(a) providing a surgical instrument having a working tip and comprising: an irrigation tube having defined therein an irrigation port at the working tip of the instrument; an aspiration mbe having defined therein an aspiration port at the working tip of the instrument; and a rotary cutting bit arranged externally of the instrument at its working tip and coupled to a rotary drive shaft disposed outside the aspiration mbe, the irrigation and aspiration ports being arranged such that in use irrigation fluid flows from the irrigation port, over and around the cutting bit and into the aspiration port, (b) making incisions in tissue to the anterior of the lens to enable access of the working tip of the cannula to the lens,

(c) contacting the lens with the cutting bit of the cannula, and

(d) causing the cutting bit to rotate whilst it is applied to the lens, irrigation fluid is passed through said irrigation mbe, and irrigation fluid and debris is aspirated through said aspiration tube.